/Engine/Source/Runtime/Engine/Public/Materials/MaterialAttributeDefinitionMap.h
Appends a new attribute definition to the custom output list
static void AddCustomAttribute ( const [FGuid](API\Runtime\Core\Misc\FGuid) & AttributeID, const [FString](API\Runtime\Core\Containers\FString) & AttributeName, const [FString](API\Runtime\Core\Containers\FString) & FunctionName, EMaterialValueType ValueType, const FVector4 & DefaultValue, MaterialAttributeBlendFunction BlendFunction )